Born the fourth boy of an eight-child, old-but-poor family from Normandy, Marigny was destined to an ecclesiastic career; he was soon sent to Sées seminary.

However, his temperament inclined him more to adventure; and at age 14 he escaped the seminary to find refuge with his older brother, Augustin Etienne Gaspard Bernard de Marigny, who was a Garde-Marine in Rochefort.

After 40 months, Marigny returned to France on Zodiaque, and served successively on Glorieux, Minotaure, Union, the frigate Légère and the fluyt Garonne.

In 1775, Marigny was awarded the Order of Saint Louis and given command of the corvette Serin, and of the station of Windward Islands.

Poisoned by sleeping on his freshly repainted ship, Marigny fell ill for one year and had to resign his command.